Lubricating oil composition for internal combustion engines and method for producing the same

ABSTRACT

A lubricating oil composition for internal combustion engines, including a lubricant base oil and 3% by mass or more, but less than 40% by mass of a liquid random copolymer of ethylene and an α-olefin, the liquid random copolymer being produced using a specific catalyst, wherein the lubricating oil composition has a kinematic viscosity at 100° C. of 6.9 mm2/s or more, but less than 12.5 mm2/s, and wherein the lubricant base oil consists of a mineral oil having a kinematic viscosity at 100° C. of 2 to 7 mm2/s, a viscosity index of 105 or more and a pour point of −10° C. or lower, and/or a synthetic oil having a kinematic viscosity at 100° C. of 1 to 7 mm2/s, a viscosity index of 120 or more and a pour point of −30° C. or lower.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition forinternal combustion engines and a method for producing the same.

BACKGROUND ART

Petroleum products generally have the so-called viscosity temperaturedependency, in which viscosity varies greatly with temperature change.For example, in lubricating oil and the like, which is used inautomobiles etc., a small viscosity temperature dependency is preferred.Thus, in lubricating oil, certain types of polymers soluble inlubricating oil bases have been utilized as viscosity modifying agents(also called viscosity index improving agents), with the objective ofreducing the viscosity temperature dependency. In recent years, OCPs(olefin copolymers) have been widely utilized as such viscositymodifying agents, and there have been a variety of improvements to OCPin order to further improve the performance of lubricating oil, asexemplified in Patent Literature 1.

Meanwhile, amidst the increased demands in recent years for theenvironmental burden to be reduced in automobiles, there is strongdemand for improvements in the fuel consumption of automobiles. Fuelconsumption improvement technology of engine oil is one of suchcountermeasures, where the lowering of the viscosity of engine oil hasbeen in progress, with the objective of reducing torque by the loweredviscosity. However, an increased risk of metal contact has beenindicated under the reduced lubricity in conjunction with the loweredviscosity of engine oil; namely under the high shear conditions of theengine oil. Therefore, the lower limit of the high shear viscosity at150° C. (High Temperature High Shear viscosity; HTHS viscosity) asmeasured by the method described in ASTM D4683, has been established inthe engine oil viscosity standards by the SAE (Society of AutomotiveEngineers) as shown in Table 1.

Viscosity modifying agents are utilized in engine oil so that thelubricating oil maintains an optimal viscosity at high temperatures.However, the molecular weight of general viscosity index improvingagents is comparatively high, and the molecular orientation of theviscosity modifying agent occurs due to shear stress, which tends tocause viscosity reduction of the lubricating oil. Therefore, there was aproblem in that the kinematic viscosity at 100° C. of the engine oil perse needed to be raised when utilizing high molecular weight viscositymodifying agents, because of the rise in HTHS viscosity.

Meanwhile, even though viscosity reduction due to shearing can besuppressed in low molecular weight viscosity modifying agents, theviscosity index improvement performance worsens, and thus,low-temperature viscosity properties are poor compared to the case ofutilizing high molecular weight viscosity modifying agents, and hence itwas difficult to realize a multi-grade viscosity modifying agent.

Patent Literature 2 discloses a lubricating oil composition containing aspecific lubricant base oil and a specific ethylene-α-olefin copolymer,which is capable of maintaining a high HTHS viscosity with lowviscosity, and which is suitably applicable to internal combustionengines.

Moreover, Patent Literature 3 describes a method for producing a liquidrandom copolymer of ethylene and α-olefin, wherein further described isthat this copolymer is useful as a lubricating oil.

TABLE 1 Viscosity Kinematic viscosity at HTHS standard ^(*1) CCSViscosity ^(*2) MR viscosity ^(*3) 100° C. ^(*4) viscosity ^(*5)Measured Upper limit Measured Upper limit Lower limit Upper limit Lowerlimit temperature viscosity temperature viscosity viscosity viscosityviscosity ° C. mPa·s ° C. mPa·s mm²/s mm²/s mPa·s  0 W −35 6,200 −4060,000 3.8  5 W −30 6,600 −35 60,000 3.8 10 W −25 7,000 −30 60,000 4.120 Not prescribed 6.9 <9.3 2.6 30 9.3 <12.5 2.9 ^(*1): Gear oils whichsatisfy the viscosity standards in the Table are described asmulti-grade gear oil with both viscosity standards. For example, thedescription 0W-20 is indicated when the standards 0 W and 20 in thetable are satisfied. ^(*2): Cold Cranking Simulator viscosity, measuredin accordance with ASTM D5293 ^(*3): Mini Rotary viscosity, measured inaccordance with ASTM D4684 ^(*4): Measured in accordance with ASTM D445^(*5): Measured in accordance with ASTM D4683

CITATION LIST Patent Literature

-   Patent Literature 1: WO 00/034420 A1-   Patent Literature 2: JP 2016-098341 A-   Patent Literature 3: EP 2921509 A1

SUMMARY OF INVENTION Technical Problem

However, there was further room for improvement in conventionallubricating oil compositions, from the perspective of providing alubricating oil composition for internal combustion engines, which iscapable of maintaining a high HTHS viscosity with low viscosity, andfurther has excellent thermal and oxidation stability.

Solution to Problem

The present inventors keenly investigated the development of alubricating oil composition having excellent performance, and as aresult, discovered that the aforementioned problem can be solved with alubricating oil composition which contains, with a specific lubricantbase oil, an ethylene-α-olefin copolymer prepared by means of a specificcatalyst, and satisfies specific conditions, thus arriving at theperfection of the present invention. The present invention specificallymentions the below aspect.

[1]

A lubricating oil composition for internal combustion engines,comprising a lubricant base oil, and 3% by mass or more, but less than40% by mass of a liquid random copolymer (C) of ethylene and α-olefin,the liquid random copolymer (C) being prepared by the below method (α),the lubricating oil composition having a kinematic viscosity at 100° C.of 6.9 mm²/s or more, but less than 12.5 mm²/s,

wherein the lubricant base oil consists of a mineral oil (A) having theproperties of the below (A1) to (A3), and/or a synthetic oil (B) havingthe properties of the below (B1) to (B3).

(A1) The mineral oil has a kinematic viscosity at 100° C. of 2 to 7mm²/s.(A2) The mineral oil has a viscosity index of 105 or more.(A3) The mineral oil has a pour point of −10° C. or lower.(B1) The synthetic oil has a kinematic viscosity at 100° C. of 1 to 7mm²/s.(B2) The synthetic oil has a viscosity index of 120 or more.(B3) The synthetic oil has a pour point of −30° C. or lower.

(Method (α))

A method (α) for preparing a liquid random copolymer of ethylene andα-olefin, comprising a step of carrying out solution polymerization ofethylene and α-olefin having 3 to 20 carbon atoms, under a catalystsystem comprising

(a) a bridged metallocene compound represented by the following Formula1, and(b) at least one compound selected from a group consisting of

(i) an organoaluminum oxy-compound, and

(ii) a compound which reacts with the bridged metallocene compound toform an ion pair.

[In Formula 1, R¹, R², R³, R⁴, R⁵, R⁸, R⁹ and R¹² are respectively andindependently hydrogen atom, hydrocarbon group or silicon-containinghydrocarbon group, and adjoining groups are optionally connected to eachother to form a ring structure,

R⁶ and R¹¹, being the same, are hydrogen atom, hydrocarbon group orsilicon-containing hydrocarbon group,

R⁷ and R¹⁰, being the same, are hydrogen atom, hydrocarbon group orsilicon-containing hydrocarbon group,

R⁶ and R⁷ are optionally connected to hydrocarbon having 2 to 3 carbonatoms to form a ring structure,

R¹¹ and R¹⁰ are optionally connected to hydrocarbon having 2 to 3 carbonatoms to form a ring structure,

R⁶, R⁷, R¹⁰ and R¹¹ are not hydrogen atom at the same time;

Y is a carbon atom or silicon atom;

R¹³ and R¹⁴ are independently aryl group;

M is Ti, Zr or Hf;

Q is independently halogen, hydrocarbon group, an anionic ligand or aneutral ligand which can be coordinated to a lone pair of electrons; and

j is an integer of 1 to 4.]

[2]

The lubricating oil composition for internal combustion engines of theaforementioned [1], wherein in the metallocene compound represented bythe above Formula 1, at least one among substituents (R¹, R², R³ and R⁴)bonded to a cyclopentadienyl group is a hydrocarbon group having 4 ormore carbon atoms.

[3]

The lubricating oil composition for internal combustion engines of theaforementioned [1] or [2], wherein R⁶ and R¹¹, being the same, arehydrocarbon groups having 1 to 20 carbon atoms.

[4]

The lubricating oil composition for internal combustion engines of anyof the aforementioned [1] to [3], wherein in the metallocene compoundrepresented by the above Formula 1, substituent (R² or R³) bonded to the3-position of the cyclopentadienyl group is a hydrocarbon group.

[5]

The lubricating oil composition for internal combustion engines of theaforementioned [4], wherein in the metallocene compound represented bythe above Formula 1, the hydrocarbon group (R² or R³) bonded to the3-position of the cyclopentadienyl group is an n-butyl group.

[6]

The lubricating oil composition for internal combustion engines of anyof the aforementioned [1] to [5], wherein in the metallocene compoundrepresented by the above Formula 1, substituents (R⁶ and R¹¹) bonded tothe 2-position and 7-position of the fluorenyl group are all tert-butylgroups.

[7]

The lubricating oil composition for internal combustion engines of anyof the aforementioned [1] to [6], wherein the compound which reacts withthe bridged metallocene compound to form an ion pair is a compoundrepresented by the following Formula 6.

[In Formula 6, R^(e+) is H⁺, a carbenium cation, an oxonium cation, anammonium cation, a phosphonium cation, a cycloheptyltrienyl cation, or aferrocenium cation having a transition metal, and R^(f) to R^(i) each isindependently a hydrocarbon group having 1 to 20 carbon atoms.]

[8]

The lubricating oil composition for internal combustion engines of theaforementioned [7], wherein the ammonium cation is a dimethylaniliniumcation.

[9]

The lubricating oil composition for internal combustion engines of theaforementioned [7] or [8], wherein the catalyst system further comprisesan organoaluminum compound selected from a group consisting of trimethylaluminum and triisobutyl aluminum.

[10]

The lubricating oil composition for internal combustion engines of anyof the aforementioned [1] to [9], wherein the α-olefin of the liquidrandom copolymer (C) is propylene.

[11]

A lubricating oil composition for internal combustion engines,comprising a lubricant base oil, and 3% by mass or more, but less than40% by mass of a liquid random copolymer of ethylene and α-olefin, theliquid random copolymer having the properties of the below (C1) to (C5),the lubricating oil composition having a kinematic viscosity at 100° C.of 6.9 mm²/s or more, but less than 12.5 mm²/s, wherein the lubricantbase oil consists of a mineral oil (A) having the properties of thebelow (A1) to (A3), and/or a synthetic oil (B) having the properties ofthe below (B1) to (B3).

(A1) The mineral oil has a kinematic viscosity at 100° C. of 2 to 7mm²/s.(A2) The mineral oil has a viscosity index of 105 or more.(A3) The mineral oil has a pour point of −10° C. or lower.(B1) The synthetic oil has a kinematic viscosity at 100° C. of 1 to 7mm²/s.(B2) The synthetic oil has a viscosity index of 120 or more.(B3) The synthetic oil has a pour point of −30° C. or lower.(C1) The liquid random copolymer comprises 40 to 60 mol % of ethyleneunits and 60 to 40 mol % of α-olefin units having 3 to 20 carbon atoms.(C2) The liquid random copolymer has a number average molecular weight(Mn) of 500 to 10,000 and a molecular weight distribution (Mw/Mn, Mw isthe weight average molecular weight) of 3 or less, as measured by GelPermeation Chromatography (GPC).(C3) The liquid random copolymer has a kinematic viscosity at 100° C. of30 to 5,000 mm²/s.(C4) The liquid random copolymer has a pour point of 30 to −45° C.(C5) The liquid random copolymer has a Bromine Number of 0.1 g/100 g orless.[12]

The lubricating oil composition for internal combustion engines of anyof the aforementioned [1] to [11], wherein the synthetic oil (B)contains an ester, and a synthetic oil other than esters.

[13]

A method for producing a lubricating oil composition for internalcombustion engines, comprising the steps of:

preparing a liquid random copolymer (C) of ethylene and α-olefin by thefollowing method (α); and

preparing a lubricating oil composition for internal combustion enginesby mixing a lubricant base oil and the liquid random copolymer (C) of anamount of 3% by mass or more, but less than 40% by mass in thelubricating oil composition, the composition having a kinematicviscosity at 100° C. of 6.9 mm²/s or more, but less than 12.5 mm²/s,

wherein the lubricant base oil consists of a mineral oil (A) having theproperties of the below (A1) to (A3), and/or a synthetic oil (B) havingthe properties of the below (B1) to (B3).

(A1) The mineral oil has a kinematic viscosity at 100° C. of 2 to 7mm²/s.(A2) The mineral oil has a viscosity index of 105 or more.(A3) The mineral oil has a pour point of −10° C. or lower.(B1) The synthetic oil has a kinematic viscosity at 100° C. of 1 to 7mm²/s.(B2) The synthetic oil has a viscosity index of 120 or more.(B3) The synthetic oil has a pour point of −30° C. or lower.

(Method (α))

A method (α) for preparing a liquid random copolymer of ethylene andα-olefin, comprising a step of carrying out solution polymerization ofethylene and α-olefin having 3 to 20 carbon atoms, under a catalystsystem comprising

(a) a bridged metallocene compound represented by the following Formula1, and(b) at least one compound selected from a group consisting of

(i) an organoaluminum oxy-compound, and

(ii) a compound which reacts with the bridged metallocene compound toform an ion pair.

[In Formula 1, R¹, R², R³, R⁴, R⁵, R⁸, R⁹ and R¹² are respectively andindependently hydrogen atom, hydrocarbon group or silicon-containinghydrocarbon group, and adjoining groups are optionally connected to eachother to form a ring structure,

R⁶ and R¹¹, being the same, are hydrogen atom, hydrocarbon group orsilicon-containing hydrocarbon group,

R⁷ and R¹⁰, being the same, are hydrogen atom, hydrocarbon group orsilicon-containing hydrocarbon group,

R⁶ and R⁷ are optionally connected to hydrocarbon having 2 to 3 carbonatoms to form a ring structure,

R¹¹ and R¹⁰ are optionally connected to hydrocarbon having 2 to 3 carbonatoms to form a ring structure,

R⁶, R⁷, R¹⁰ and R¹¹ are not hydrogen atom at the same time;

Y is a carbon atom or silicon atom;

R¹³ and R¹⁴ are independently aryl group;

M is Ti, Zr or Hf;

Q is independently halogen, hydrocarbon group, an anionic ligand or aneutral ligand which can be coordinated to a lone pair of electrons; and

j is an integer of 1 to 4.]

Advantageous Effects of Invention

The lubricating oil composition of the present invention is capable ofmaintaining a high HTHS viscosity, contributes to better fuel efficiencyof internal combustion engine oil due to low kinematic viscosity at 100°C., and further has excellent thermal and oxidation stability.

DESCRIPTION OF EMBODIMENTS

The lubricating oil composition for internal combustion enginesaccording to the present invention (hereinafter, also referred to merelyas “lubricating oil composition”) will be explained in detail below.

The lubricating oil composition for internal combustion enginesaccording to the present invention comprises a lubricant base oil, and3% by mass or more, but less than 40% by mass of a liquid randomcopolymer (C) of ethylene and α-olefin prepared by method (α) (may alsobe described in the present specification as “ethylene-α-olefincopolymer (C)”), the lubricating oil composition having a kinematicviscosity at 100° C. of 6.9 mm²/s or more, but less than 12.5 mm²/s,where the lubricant base oil consists of a mineral oil (A) and/orsynthetic oil (B).

<Lubricant Base Oil>

In the lubricant base oil used in the present invention, performance andquality such as viscosity properties, heat resistance and oxidationstability, will differ depending on the producing and refining processesetc. of the lubricant base oil. The API (American Petroleum Institute)categorizes lubricant base oil into five types: Group I, II, III, IV andV. These API categories are defined in the API Publication 1509, 15thEdition, Appendix E, April 2002, and are as shown in Table 2.

TABLE 2 Saturated hydrocarbon Sulfur Viscosity portion ^(*2) portion^(*3) Group Type index ^(*1) (vol %) (% by weight) I Mineral 80 to 120<90 >0.03 oil II Mineral 80 to 120 ≥90 ≤0.03 oil III Mineral ≥120 ≥90≤0.03 oil IV poly-α-olefin V Lubricant base material other than theaforementioned ^(*1) Measured in accordance with ASTM D445 (JIS K2283)^(*2) Measured in accordance with ASTM D3238 ^(*3) Measured inaccordance with ASTM D4294 (JIS K2541) *4: Mineral oils whose saturatedhydrocarbon portion is less than 90 vol % and sulfur portion is lessthan 0.03% by weight, or whose saturated hydrocarbon portion is 90 vol %or more and sulfur portion exceeds 0.03% by weight, are included inGroup I.

<(A) Mineral Oil>

The mineral oil (A) has the properties of (A1) to (A3) below. Themineral oil (A) in the present invention is ascribed to Groups I to IIIof the aforementioned API categories.

(A1) The mineral oil has a kinematic viscosity at 100° C. of 2 to 7mm²/s

The value of this kinematic viscosity is that as measured in accordancewith the method described in JIS K2283. The kinematic viscosity at 100°C. of mineral oil (A) is 2 to 7 mm²/s, preferably 2.5 to 7.0 mm²/s, andmore preferably 3.5 to 6.5 mm²/s. With a kinematic viscosity at 100° C.in this range, the lubricating oil composition of the present inventionis excellent in terms of volatility and temperature viscosityproperties.

(A2) The Mineral Oil has a Viscosity Index of 105 or More

The value of this viscosity index is that as measured in accordance withthe method described in JIS K2283. The viscosity index of mineral oil(A) is 105 or more, preferably 115 or more, and more preferably 120 ormore. With a viscosity index in this range, the lubricating oilcomposition of the present invention has excellent temperature viscosityproperties.

(A3) The Mineral Oil has a Pour Point of −10° C. or Lower

The value of this pour point is that as measured in accordance with themethod described in ASTM D97. The pour point of mineral oil (A) is −10°C. or lower, and preferably −12° C. or lower. With a pour point in thisrange, the lubricating oil composition of the present invention hasexcellent low-temperature viscosity properties, when using the mineraloil (A) together with a pour point lowering agent.

The quality of the mineral oil is as mentioned above, where theaforementioned respective qualities of mineral oil are obtainabledepending on the refining method. Exemplifications of the mineral oil(A) specifically include: a lubricant base oil, in which a lubricatingoil fraction obtained by reduced pressure distillation of an atmosphericresidue which is obtainable by the atmospheric distillation of crudeoil, is refined by one or more treatments such as solvent deasphalting,solvent extraction, hydrocracking, solvent dewaxing, hydrorefining; or alubricant base oil of wax isomerized mineral oil.

Moreover, a Gas-to-Liquid (GTL) base oil obtained by the Fisher-Tropschmethod is a base oil which can also be suitably utilized as Group IIImineral oil. Such GTL base oil is also handled as Group III+ lubricantbase oil, which are described e.g. in the following Patent Literatures:EP0776959, EP0668342, WO97/21788, WO00/15736, WO00/14188, WO00/14187,WO00/14183, WO00/14179, WO00/08115, WO99/41332, EP1029029, WO01/18156and WO01/57166.

In the lubricating oil composition of the present invention, the mineraloil (A) may be used alone as a lubricant base oil, or any mixture etc.of two or more lubricating oils selected from the synthetic oil (B) andthe mineral oil (A) may be used as a lubricant base oil.

<(B) Synthetic Oil>

The synthetic oil (B) has the characteristics of (B1) to (B3) below. Thesynthetic oil (B) in the present invention is ascribed to Group IV orGroup V in the aforementioned API categories.

(B1) The Synthetic Oil has a Kinematic Viscosity at 100° C. of 1 to 7mm²/s

The value of this kinematic viscosity is that as measured in accordancewith the method described in JIS K2283. The kinematic viscosity at 100°C. of synthetic oil (B) is 1 to 7 mm²/s, preferably 2.0 to 7.0 mm²/s,and more preferably 3.5 to 6.0 mm²/s. With a kinematic viscosity at 100°C. in this range, the lubricating oil composition of the presentinvention is excellent in terms of volatility and temperature viscosityproperties.

(B2) The Synthetic Oil has a Viscosity Index of 120 or More

The value of this viscosity index is that as measured in accordance withthe method described in JIS K2283. The viscosity index of synthetic oil(B) is 120 or more, and preferably 123 or more. With a viscosity indexin this range, the lubricating oil composition of the present inventionhas excellent temperature viscosity properties.

(B3) The Synthetic Oil has a Pour Point of −30° C. or Lower

The value of this pour point is that as measured in accordance with themethod described in ASTM D97. The pour point of synthetic oil (B) is−30° C. or lower, preferably −40° C. or lower, more preferably −50° C.or lower, and furthermore preferably −60° C. or lower. With a pour pointin this range, the lubricating oil composition of the present inventionhas excellent low-temperature viscosity properties.

Poly-α-olefins, which are ascribed to Group IV, can be obtained byoligomerizing higher α-olefins with an acid catalyst, as described ine.g. U.S. Pat. Nos. 3,780,128, 4,032,591, and JP H01-163136 A. Of these,a low molecular weight oligomer of at least one olefin selected from anolefin having 8 or more carbon atoms can be utilized as thepoly-α-olefin. If utilizing a poly-α-olefin as the lubricant base oil, alubricating oil composition having remarkably excellent temperatureviscosity properties, low-temperature viscosity properties, as well asheat resistance is obtainable.

Poly-α-olefins are also industrially available, where those with akinematic viscosity at 100° C. of 2 mm²/s to 6 mm²/s are commerciallyavailable. Examples include the NEXBASE 2000 series (made by NESTE),Spectrasyn (made by ExxonMobil Chemical), Durasyn (made by INEOSOligomers), and Synfluid (made by Chevron Phillips Chemical).

As the synthetic oil ascribed to Group V, examples include alkylbenzenes, alkyl naphthalenes, isobutene oligomers and hydrides thereof,paraffins, polyoxy alkylene glycol, dialkyl diphenylether,polyphenylether, and esters.

Most of the alkyl benzenes and alkyl naphthalenes are usually dialkylbenzene or dialkyl naphthalene whose alkyl chain length has 6 to 14carbon atoms, where such alkyl benzenes or alkyl naphthalenes areproduced by the Friedel-Crafts alkylation reaction of benzene ornaphthalene with olefin. In the production of alkyl benzenes or alkylnaphthalenes, the alkylated olefin to be utilized may be a linear orbranched olefin, or may be a combination of these. These productionprocesses are described in e.g. U.S. Pat. No. 3,909,432.

Moreover, as the ester, fatty acid esters are preferred from theperspective of compatibility with the ethylene-α-olefin copolymer (C).

Although there are no particular limitations on the fatty acid esters,examples include fatty acid esters consisting of only carbon, oxygen orhydrogen as mentioned below, where the examples include monoestersprepared from a monobasic acid and alcohol; diesters prepared fromdibasic acid and alcohol, or from a diol with a monobasic acid or anacid mixture; or polyolesters prepared by reacting a monobasic acid oran acid mixture with a diol, triol (e.g. trimethylolpropane), tetraol(e.g. pentaerythritol), hexol (e.g. dipentaerythritol) etc. Examples ofthese esters include ditridecyl glutarate, di-2-ethyl hexyl adipate,diisodecyl adipate, ditridecyl adipate, di-2-ethyl hexyl sebacate,tridecyl pelargonate, di-2-ethyl hexyl adipate, di-2-ethyl hexylazelate, trimethylolpropane caprylate, trimethylolpropane pelargonate,trimethylolpropane triheptanoate, pentaerythritol-2-ethyl hexanoate,pentaerythritol pelargonate, and pentaerythritol tetraheptanoate.

From the perspective of the compatibility with the ethylene-α-olefincopolymer (C), an alcohol having two or more functional hydroxyl groupsis preferred as the alcohol moiety constituting the ester, and a fattyacid having 8 or more carbon atoms is preferred as the fatty acidmoiety. However, a fatty acid having 20 or fewer carbon atoms, which iseasily industrially available, is superior in terms of the manufacturingcost of the fatty acid. The effect of the present invention is alsosufficiently exhibited with the use of one fatty acid constituting anester, or with the use of a fatty acid ester prepared by means of two ormore acid mixtures. Examples of fatty acid esters more specificallyinclude a mixed triester of trimethylolpropane with lauric acid andstearic acid, and diisodecyl adipate, where these are preferable interms of compatibility of saturated hydrocarbon components such as theethylene-α-olefin copolymer (C), with antioxidants, corrosion preventingagents, anti-wear agents, friction modifying agents, pour point loweringagents, anti-rust agents and anti-foamers mentioned below and having apolar group.

When utilizing a synthetic oil (B), particularly a poly-α-olefin as alubricant base oil, it is preferable that the lubricating oilcomposition of the present invention contain a fatty acid ester in anamount of 5 to 20% by mass with respect to 100% by mass of the entireweight of the lubricating oil composition. By containing a fatty acidester of 5% by mass or more, good compatibility is obtainable with thelubricating oil sealing material such as resins and elastomers insidethe internal combustion engines and industrial machinery of all types.Specifically, swelling of the lubricating oil sealing material can besuppressed. From the perspective of oxidation stability or heatresistance, the amount of ester is preferably 20% by mass or less. Whenmineral oil is contained in the lubricating oil composition, a fattyacid ester is not necessarily required, because the mineral oil per sehas a swelling suppression effect of the lubricating oil sealing agent.

<(C) Ethylene-α-Olefin Copolymer>

The ethylene-α-olefin copolymer (C) is a liquid random copolymer (C) ofethylene and α-olefin prepared by the following method (α).

(Method (α))

A method (α) for preparing a liquid random copolymer of ethylene andα-olefin, comprising a step of carrying out solution polymerization ofethylene and α-olefin having 3 to 20 carbon atoms, under a catalystsystem containing

(a) a bridged metallocene compound represented by the following Formula1, and(b) at least one compound selected from a group consisting of

(i) an organoaluminum oxy-compound, and

(ii) a compound which reacts with the bridged metallocene compound toform an ion pair.

[In Formula 1, R¹, R², R³, R⁴, R⁵, R⁸, R⁹ and R¹² are respectively andindependently hydrogen atom, hydrocarbon group or silicon-containinghydrocarbon group, and adjoining groups are optionally connected to eachother to form a ring structure,

R⁶ and R¹¹, being the same, are hydrogen atom, hydrocarbon group orsilicon-containing hydrocarbon group,

R⁷ and R¹⁰, being the same, are hydrogen atom, hydrocarbon group orsilicon-containing hydrocarbon group,

R⁶ and R⁷ are optionally connected to hydrocarbon having 2 to 3 carbonatoms to form a ring structure,

R¹¹ and R¹⁰ are optionally connected to hydrocarbon having 2 to 3 carbonatoms to form a ring structure,

R⁶, R⁷, R¹⁰ and R¹¹ are not hydrogen atom at the same time;

Y is a carbon atom or silicon atom;

R¹³ and R¹⁴ are independently aryl group;

M is Ti, Zr or Hf;

Q is independently halogen, hydrocarbon group, an anionic ligand or aneutral ligand which can be coordinated to a lone pair of electrons; and

j is an integer of 1 to 4.]

Here, the hydrocarbon group has 1 to 20 carbon atoms, preferably 1 to 15atoms, and more preferably 4 to 10 carbon atoms, and means for examplean alkyl group, aryl group etc. The aryl group has 6 to 20 carbon atoms,and preferably 6 to 15 carbon atoms.

Examples of the silicon-containing hydrocarbon group include an alkyl oraryl group having 3 to 20 carbon atoms which contains 1 to 4 siliconatoms, and in more detail includes trimethylsilyl group,tert-butyldimethylsilyl group, triphenylsilyl group etc.

In the bridged metallocene compound represented by Formula 1,cyclopentadienyl group may be substituted or unsubstituted.

In the bridged metallocene compound represented by Formula 1,

(i) it is preferable that at least one among substituents (R¹, R², R³and R⁴) bonded to cyclopentadienyl group is a hydrocarbon group,

(ii) it is more preferable that at least one among substituents (R¹, R²,R³ and R⁴) is a hydrocarbon group having 4 or more carbon atoms,

(iii) it is most preferable that substituent (R² or R³) bonded to the3-position of the cyclopentadienyl group is a hydrocarbon group having 4or more carbon atoms (for example an n-butyl group).

In case where at least two among R¹, R², R³ and R⁴ are substituents(that is, being not hydrogen atom), the above-mentioned substituents maybe the same or be different, and it is preferable that at least onesubstituent is a hydrocarbon group having 4 or more carbon atoms.

In the metallocene compound represented by Formula 1, R⁶ and R¹¹ bondedto fluorenyl group are the same, R⁷ and R¹⁰ are the same, but R⁶, R⁷,R¹⁰ and R¹¹ are not hydrogen atom at the same time. In high-temperaturesolution polymerization of poly-α-olefin, in order to improve thepolymerization activity, preferably neither R⁶ nor R¹¹ is hydrogen atom,and more preferably none of R⁶, R⁷, R¹⁰ and R¹¹ is hydrogen atom. Forexample, R⁶ and R¹¹ bonded to the 2-position and 7-position of thefluorenyl group are the same hydrocarbon group having 1 to 20 carbonatoms, and preferably all tert-butyl groups, and R⁷ and R¹⁰ are the samehydrocarbon group having 1 to 20 carbon atoms, and preferably alltert-butyl groups.

The main chain part (bonding part, Y) connecting the cyclopentadienylgroup and the fluorenyl group is a cross-linking section of two covalentbonds comprising one carbon atom or silicon atom, as a structural bridgesection imparting steric rigidity to the bridged metallocene compoundrepresented by Formula 1. Cross-linking atom (Y) in the cross-linkingsection has two aryl groups (R¹³ and R¹⁴) which may be the same ordifferent. Therefore, the cyclopentadienyl group and the fluorenyl groupare bonded by the covalent bond cross-linking section containing an arylgroup. Examples of the aryl group include a phenyl group, naphthylgroup, anthracenyl group, and a substituted aryl group (which is formedby substituting one or more aromatic hydrogen (sp²-type hydrogen) of aphenyl group, naphthyl group or anthracenyl group, with substituents).Examples of substituents in the aryl group include a hydrocarbon grouphaving 1 to 20 carbon atoms, a silicon-containing hydrocarbon grouphaving 1 to 20 carbon atoms, a halogen atom etc., and preferably includea phenyl group. In the bridged metallocene compound represented byFormula 1, preferably R¹³ and R¹⁴ are the same in view of easyproduction.

In the bridged metallocene compound represented by Formula 1, Q ispreferably a halogen atom or hydrocarbon group having 1 to 10 carbonatoms. The halogen atom includes fluorine, chlorine, bromine or iodine.The hydrocarbon group having 1 to 10 carbon atoms includes methyl,ethyl, n-propyl, isopropyl, 2-methylpropyl, 1,1-dimethylpropyl,2,2-dimethylpropyl, 1,1-diethylpropyl, 1-ethyl-1-methylpropyl,1,1,2,2-tetramethylpropyl, sec-butyl, tert-butyl, 1,1-dimethylbutyl,1,1,3-trimethylbutyl, neopentyl, cyclohexyl methyl, cyclohexyl,1-methyl-1-cyclohexyl etc. Further, when j is an integer of 2 or more, Qmay be the same or different.

Examples of such bridged metallocene compounds (a) include:

ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (η⁵-fluorenyl)zirconium dichloride, ethylene [η⁵-(3-tert-butyl-5-methylcyclopentadienyl)] [η⁵-(3,6-di-tert-butyl fluorenyl)] zirconiumdichloride, ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(2,7-di-tert-butyl fluorenyl)] zirconium dichloride, ethylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (octamethyloctahydrodibenzofluorenyl) zirconium dichloride, ethylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (benzofluorenyl) zirconiumdichloride, ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)](dibenzofluorenyl) zirconium dichloride, ethylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)](octahydrodibenzofluorenyl) zirconium dichloride, ethylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride,ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride;

ethylene [η⁵-(3-tert-butyl cyclopentadienyl)] (η⁵-fluorenyl) zirconiumdichloride, ethylene [η⁵-(3-tert-butyl cyclopentadienyl)][η⁵-(3,6-di-tert-butyl fluorenyl)] zirconium dichloride, ethylene[η⁵-(3-tert-butyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butyl fluorenyl)]zirconium dichloride, ethylene [η⁵-(3-tert-butyl cyclopentadienyl)](octamethyl octahydrodibenzofluorenyl) zirconium dichloride, ethylene[η⁵-(3-tert-butyl cyclopentadienyl)] (benzofluorenyl) zirconiumdichloride, ethylene [η⁵-(3-tert-butyl cyclopentadienyl)](dibenzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-tert-butylcyclopentadienyl)] (octahydrodibenzofluorenyl) zirconium dichloride,ethylene [η⁵-(3-tert-butyl cyclopentadienyl)][η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride,ethylene [η⁵-(3-tert-butyl cyclopentadienyl)][η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride;ethylene [η⁵-(3-n-butyl cyclopentadienyl)] (η⁵-fluorenyl) zirconiumdichloride, ethylene [η⁵-(3-n-butyl cyclopentadienyl)][η⁵-(3,6-di-tert-butyl fluorenyl)] zirconium dichloride, ethylene[η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butyl fluorenyl)]zirconium dichloride, ethylene [η⁵-(3-n-butyl cyclopentadienyl)](octamethyl octahydrodibenzofluorenyl) zirconium dichloride, ethylene[η⁵-(3-n-butyl cyclopentadienyl)] (benzofluorenyl) zirconium dichloride,ethylene [η⁵-(3-n-butyl cyclopentadienyl)] (dibenzofluorenyl) zirconiumdichloride, ethylene [η⁵-(3-n-butyl cyclopentadienyl)](octahydrodibenzofluorenyl) zirconium dichloride, ethylene[η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(2,7-diphenyl-3,6-di-tert-butylfluorenyl)] zirconium dichloride, ethylene [η⁵-(3-n-butylcyclopentadienyl)] [η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)]zirconium dichloride;

diphenylmethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)](η⁵-fluorenyl) zirconium dichloride, diphenylmethylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] [η⁵-(3,6-di-tert-butylfluorenyl)] zirconium dichloride, diphenylmethylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butylfluorenyl)] zirconium dichloride, diphenylmethylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (octamethyloctahydrodibenzofluorenyl) zirconium dichloride, diphenylmethylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (benzofluorenyl) zirconiumdichloride, diphenylmethylene [η⁵-(3-tert-butyl-5-methylcyclopentadienyl)] (dibenzofluorenyl) zirconium dichloride,diphenylmethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)](octahydrodibenzofluorenyl) zirconium dichloride, diphenylmethylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride,diphenylmethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride;

diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)] (η⁵-fluorenyl)zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butylcyclopentadienyl)] [η⁵-(3,6-di-tert-butyl fluorenyl)] zirconiumdichloride, diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)][η⁵-(2,7-di-tert-butyl fluorenyl)] zirconium dichloride,diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)] (octamethyloctahydrodibenzofluorenyl) zirconium dichloride, diphenylmethylene[η⁵-(3-tert-butyl cyclopentadienyl)] (benzofluorenyl) zirconiumdichloride, diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)](dibenzofluorenyl) zirconium dichloride, diphenylmethylene[η⁵-(3-tert-butyl cyclopentadienyl)] (octahydrodibenzofluorenyl)zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butylcyclopentadienyl)] [η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)]zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butylcyclopentadienyl)] [η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)]zirconium dichloride;

diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)] (η⁵-fluorenyl)zirconium dichloride, diphenylmethylene [η⁵-(3-n-butylcyclopentadienyl)] [η⁵-(3,6-di-tert-butyl fluorenyl)] zirconiumdichloride, diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)][η⁵-(2,7-di-tert-butyl fluorenyl)] zirconium dichloride,diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)] (octamethyloctahydrodibenzofluorenyl) zirconium dichloride, diphenylmethylene[η⁵-(3-n-butyl cyclopentadienyl)] (benzofluorenyl) zirconium dichloride,diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)] (dibenzofluorenyl)zirconium dichloride, diphenylmethylene [η⁵-(3-n-butylcyclopentadienyl)] (octahydrodibenzofluorenyl) zirconium dichloride,diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)][η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride,diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)][η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride;

di(p-tolyl) methylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)](η⁵-fluorenyl) zirconium dichloride, di(p-tolyl) methylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] [η⁵-(3,6-di-tert-butylfluorenyl)] zirconium dichloride, di(p-tolyl) methylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butylfluorenyl)] zirconium dichloride, di(p-tolyl) methylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (octamethyloctahydrodibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (benzofluorenyl) zirconiumdichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl-5-methylcyclopentadienyl)] (dibenzofluorenyl) zirconium dichloride, di(p-tolyl)methylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)](octahydrodibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene[η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride,di(p-tolyl) methylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride;

di(p-tolyl) methylene [η⁵-(3-tert-butyl cyclopentadienyl)](η⁵-fluorenyl) zirconium dichloride, di(p-tolyl) methylene[η⁵-(3-tert-butyl cyclopentadienyl)] [η⁵-(3,6-di-tert-butyl fluorenyl)]zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butylcyclopentadienyl)] [η⁵-(2,7-di-tert-butyl fluorenyl)] zirconiumdichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl cyclopentadienyl)](octamethyl octahydrodibenzofluorenyl) zirconium dichloride, di(p-tolyl)methylene [η⁵-(3-tert-butyl cyclopentadienyl)] (benzofluorenyl)zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butylcyclopentadienyl)] (dibenzofluorenyl) zirconium dichloride, di(p-tolyl)methylene [η⁵-(3-tert-butyl cyclopentadienyl)](octahydrodibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene[η⁵-(3-tert-butyl cyclopentadienyl)] [η⁵-(2,7-diphenyl-3,6-di-tert-butylfluorenyl)] zirconium dichloride, di(p-tolyl) methylene[η⁵-(3-tert-butyl cyclopentadienyl)] [η⁵-(2,7-dimethyl-3,6-di-tert-butylfluorenyl)] zirconium dichloride; and di(p-tolyl) methylene[η⁵-(3-n-butyl cyclopentadienyl)] (η⁵-fluorenyl) zirconium dichloride,di(p-tolyl) methylene [η⁵-(3-n-butyl cyclopentadienyl)][η⁵-(3,6-di-tert-butyl fluorenyl)] zirconium dichloride, di(p-tolyl)methylene [η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butylfluorenyl)] zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-n-butylcyclopentadienyl)] (octamethyl octahydrodibenzofluorenyl) zirconiumdichloride, di(p-tolyl) methylene [η⁵-(3-n-butyl cyclopentadienyl)](benzofluorenyl) zirconium dichloride, di(p-tolyl) methylene[η⁵-(3-n-butyl cyclopentadienyl)] (dibenzofluorenyl) zirconiumdichloride, di(p-tolyl) methylene [η⁵-(3-n-butyl cyclopentadienyl)](octahydrodibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene[η⁵-(3-n-butyl cyclopentadienyl)] (2,7-diphenyl-3,6-di-tert-butylfluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-n-butylcyclopentadienyl)] [η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)]zirconium dichloride.

Although compounds whose zirconium atoms were substituted with hafniumatoms, or compounds whose chloro ligands were substituted with methylgroups etc. are exemplified in these compounds, the bridged metallocenecompound (a) is not limited to these exemplifications.

As the organoaluminum oxy-compound used in the catalyst system in thepresent invention, conventional aluminoxane can be used. For example,linear or ring type aluminoxane represented by the following Formulas 2to 5 can be used. A small amount of organic aluminum compound may becontained in the organoaluminum oxy-compound.

In Formulae 2 to 4, R is independently a hydrocarbon group having 1 to10 carbon atoms, Rx is independently a hydrocarbon group having 2 to 20carbon atoms, m and n are independently an integer of 2 or more,preferably 3 or more, more preferably 10 to 70, and most preferably 10to 50.

In Formula 5, R^(c) is a hydrocarbon group having 1 to 10 carbon atoms,and R^(d) is independently a hydrogen atom, halogen atom or hydrocarbongroup having 1 to 10 carbon atoms.

In Formula 2 or Formula 3, R is a methyl group (Me) of theorganoaluminum oxy-compound which is conventionally referred to as“methylaluminoxane”.

The methylaluminoxane is easily available and has high polymerizationactivity, and thus it is commonly used as an activator in the polyolefinpolymerization. However, the methylaluminoxane is difficult to dissolvein a saturated hydrocarbon, and thus it has been used as a solution ofaromatic hydrocarbon such as toluene or benzene, which isenvironmentally undesirable. Therefore, in recent years, a flexible bodyof methylaluminoxane represented by Formula 4 has been developed andused as an aluminoxane dissolved in the saturated hydrocarbon. Themodified methylaluminoxane represented by Formula 4 is prepared by usinga trimethyl aluminum and an alkyl aluminum other than the trimethylaluminum as shown in U.S. Pat. Nos. 4,960,878 and 5,041,584, and forexample, is prepared by using trimethyl aluminum and triisobutylaluminum. The aluminoxane in which Rx is an isobutyl group iscommercially available under the trade name of MMAO and TMAO, in theform of a saturated hydrocarbon solution. (See Tosoh FinechemCorporation, Tosoh Research & Technology Review, Vol 47, 55 (2003)).

As (ii) the compound which reacts with the bridged metallocene compoundto form an ion pair (hereinafter, referred to as “ionic compound” asrequired) which is contained in the present catalyst system, a Lewisacid, ionic compounds, borane, borane compounds and carborane compoundscan be used. These are described in patent literatures, Korean PatentNo. 10-551147 A, JP H01-501950 A, JP H03-179005 A, JP H03-179006 A, JPH03-207703 A, JP H03-207704 A, U.S. Pat. No. 5,321,106 and so on. Ifneeded, heteropoly compounds, and isopoly compound etc. can be used, andthe ionic compound disclosed in JP 2004-51676 A can be used. The ioniccompound may be used alone or by mixing two or more. In more detail,examples of the Lewis acid include the compound represented by BR₃ (R isfluoride, substituted or unsubstituted alkyl group having 1 to 20 carbonatoms (methyl group, etc.), substituted or unsubstituted aryl grouphaving 6 to 20 carbon atoms (phenyl group, etc.), and also includes forexample, trifluoro boron, triphenyl boron, tris(4-fluorophenyl) boron,tris(3,5-difluorophenyl) boron, tris(4-fluorophenyl) boron,tris(pentafluorophenyl) and boron tris(p-tolyl) boron. When the ioniccompound is used, its use amount and sludge amount produced arerelatively small in comparison with the organoaluminum oxy-compound, andthus it is economically advantageous. In the present invention, it ispreferable that the compound represented by the following Formula 6 isused as the ionic compound.

In Formula 6, R^(e+) is H⁺, a carbenium cation, an oxonium cation, anammonium cation, a phosphonium cation, a cycloheptyltrienyl cation, or aferrocenium cation having a transition metal, and R^(f) to R^(i) each isindependently an organic group, preferably a hydrocarbon group having 1to 20 carbon atoms, and more preferably an aryl group, for example, apenta-fluorophenyl group. Examples of the carbenium cation include atris(methylphenyl)carbenium cation and a tris(dimethylphenyl)carbeniumcation, and examples of the ammonium cation include a dimethylaniliniumcation.

Examples of compounds represented by the aforementioned Formula 6preferably include N,N-dialkyl anilinium salts, and specifically includeN,N-dimethylanilinium tetraphenylborate, N,N-dimethylanilinium tetrakis(pentafluorophenyl) borate, N,N-dimethylanilinium tetrakis(3,5-ditrifluoro methylphenyl) borate, N,N-diethyl aniliniumtetraphenylborate, N,N-diethyl anilinium tetrakis (pentafluorophenyl)borate, N,N-diethyl anilinium tetrakis (3,5-ditrifluoro methylphenyl)borate, N,N-2,4,6-penta methylanilinium tetraphenylborate, andN,N-2,4,6-penta methylanilinium tetrakis (pentafluorophenyl) borate.

The catalyst system used in the present invention further includes (c)an organoaluminum compound when it is needed. The organoaluminumcompound plays a role of activating the bridged metallocene compound,the organoaluminum oxy-compound, and the ionic compound, etc. As theorganoaluminum compound, preferably an organoaluminum represented by thefollowing Formula 7, and alkyl complex compounds of the Group 1 metaland aluminum represented by the following Formula 8 can be used.

R^(a) _(m)Al(OR^(b))_(n)H_(p)X_(q)  Formula 7

In Formula 7, R^(a) and Rb each is independently a hydrocarbon grouphaving 1 to 15 carbon atoms, preferably 1 to 4 carbon atoms, and X is ahalogen atom, m is an integer of 0<m≤3, n is an integer of 0≤n≤, p is aninteger of 0<p≤3, q is an integer of 0≤q<3, and m+n+p+q=3.

M²AlR^(a) ₄  Formula 8

In Formula 8, M² represents Li, Na or K, and R^(a) is a hydrocarbongroup having 1 to 15 carbon atoms, and preferably 1 to 4 carbon atoms.

Examples of the organoaluminum compound represented by Formula 7 includetrimethyl aluminum and triisobutyl aluminum etc., which are easilyavailable. Examples of the alkyl complex compounds of Group 1 metal andaluminum represented by Formula 8 include LiAl(C₂H₅)₄, LiAl(C₇H₁₅)₄ etc.Compounds similar to the compounds represented by Formula 7 can be used.For example, like (C₂H₅)₂AlN(C₂H₅)Al(C₂H₅)₂, an organoaluminum compoundto which at least 2 aluminum compounds are bonded through nitrogenatoms, can be used.

In the method for preparing the ethylene-α-olefin copolymer (C), theamount of (a) the bridged metallocene compound represented by Formula 1is preferably 5 to 50% by weight with respect to total catalystcomposition. Moreover, preferably the amount of (b) (i) theorganoaluminum oxy-compound is 50 to 500 equivalent weight with respectto the molar number of the bridged metallocene compound to be used, theamount of (b) (ii) the compound which reacts with the bridgedmetallocene compound to form an ion pair is 1 to 5 equivalent weightwith respect to the molar number of bridged metallocene compound to beused, and the amount of (c) the organoaluminum compound is 5 to 100equivalent weight with respect to the molar number of the bridgedmetallocene compound to be used.

The catalyst system used in the present invention may have the following[1] to [4] for example.

[1] (a) the bridged metallocene compound represented by Formula 1, and(b) (i) the organoaluminum oxy-compound.[2] (a) the bridged metallocene compound represented by Formula 1, (b)(i) the organoaluminum oxy-compound and (c) the organoaluminum compound.[3] (a) the bridged metallocene compound represented by Formula 1, (b)(ii) the compound which reacts with the bridged metallocene compound toform an ion pair, and (c) the organoaluminum compound.[4] (a) bridged metallocene compound represented by Formula 1, and (b)(i) the organoaluminum oxy-compound and (ii) the compound which reactswith the bridged metallocene compound to form an ion pair.

(a) The bridged metallocene compound represented by Formula 1 (element(a)), (b) (i) the organoaluminum oxy-compound (element (b)), (ii) thecompound which reacts with the bridged metallocene compound to form anion pair and/or (c) the organoaluminum compound (element (c)) may beintroduced in any order, to a starting raw material monomer (a mixtureof ethylene and α-olefin having 3 to 20 carbon atoms). For example,elements (a), (b) and/or (c) are introduced alone or in any order, to apolymerization reactor with which raw material monomer is filled.Alternatively, if required, at least two elements among (a), (b) and/or(c) are mixed and then the mixed catalyst composition is introduced tothe polymerization reactor with which raw material monomer is filled.

The ethylene-α-olefin copolymer (C) is prepared by a solutionpolymerization of ethylene and α-olefin having 3 to 20 carbon atomsunder the catalyst system. As the α-olefin having 3 to 20 carbon atoms,one or more among linear α-olefins such as propylene, 1-butene,1-penetene, 1-hexene etc., branched α-olefins such as isobutylene,3-methyl-1-butene, 4-methyl-1-penetene etc. and mixtures thereof can beused. Preferably, one or more α-olefins having 3 to 6 carbon atoms canbe used, and more preferably, propylene can be used. The solutionpolymerization can be carried out by using an inert solvent such aspropane, butane or hexane etc. or an olefin monomer itself as a medium.In the copolymerization of ethylene and α-olefin of the presentinvention, the temperature for the copolymerization is conventionally 80to 150° C. and preferably 90 to 120° C., and the pressure for thecopolymerization is conventionally atmospheric pressure to 500 kgf/cm²and preferably atmospheric pressure to 50 kgf/cm², which can vary inaccordance with reacting materials, reacting conditions, etc.

Batch-, semi-continuous- or continuous-type polymerization can becarried out, and continuous-type polymerization is preferably carriedout.

The ethylene-α-olefin copolymer (C) is in liquid phase at roomtemperature, and has a structure where the α-olefin units are uniformlydistributed in the copolymer chain. The ethylene-α-olefin copolymer (C)comprises e.g. 60 to 40 mol %, preferably 45 to 55 mol %, of ethyleneunits derived from ethylene, and further comprises e.g. 40 to 60 mol %,preferably 45 to 55 mol %, of α-olefin units having 3 to 20 carbon atomswhich are derived from α-olefin having 3 to 20 carbon atoms.

The number average molecular weight (Mn) of the ethylene-α-olefincopolymer (C) is e.g. 500 to 10,000 and preferably 800 to 6,000, and themolecular weight distribution (Mw/Mn, Mw is weight average molecularweight) is e.g. 3 or less and preferably 2 or less. The number averagemolecular weight (Mn) and the molecular weight distribution (Mw/Mn) aremeasured by gel permeation chromatography (GPC).

The ethylene-α-olefin copolymer (C) has a kinematic viscosity at 100° C.of e.g. 30 to 5,000 and preferably 50 to 3,000 mm²/s, a pour point ofe.g. 30 to −45° C. and preferably 20 to −35° C., and a Bromine Number of0.1/100 g or less.

In the bridged metallocene compound represented by Formula 1, thepolymerization activity is particularly high with respect to thecopolymerization of ethylene with α-olefin. Utilizing this bridgedmetallocene compound selectively stops polymerization by hydrogenintroduction at the molecular terminals, and thus there is littleunsaturated bonding of the resulting ethylene-α-olefin copolymer (C).Moreover, since the ethylene-α-olefin copolymer (C) has a high randomcopolymerization, it has a controlled molecular weight distribution, andthus has excellent shear stability and viscosity properties. Therefore,it is considered that the lubricating oil composition for internalcombustion engines of the present invention containing theethylene-α-olefin copolymer (C) is capable of maintaining a high HTHSviscosity, contributes to better fuel efficiency of internal combustionengine oil due to low kinematic viscosity at 100° C., and further hasexcellent thermal and oxidation stability.

<Lubricating Oil Composition for Internal Combustion Engines>

The lubricating oil composition for internal combustion enginesaccording to the present invention contains a lubricant base oilconsisting of the mineral oil (A) and/or synthetic oil (B), and containsthe ethylene-α-olefin copolymer (C).

The lubricating oil composition for internal combustion enginesaccording to the present invention contains 3% by mass or more, but lessthan 40% by mass of the ethylene-α-olefin copolymer (C). If the contentof the ethylene-α-olefin copolymer (C) is less than 3% by mass, asufficient HTHS viscosity is not obtainable. If the content of theethylene-α-olefin copolymer (C) is 40% by mass or more, the fuelefficiency performance worsens.

The lubricating oil composition for internal combustion enginesaccording to the present invention has a kinematic viscosity at 100° C.of 6.9 mm²/s or more, but less than 12.5 mm²/s. The value of thiskinematic viscosity is that when measured according to the methoddescribed in JIS K2283. If the kinematic viscosity at 100° C. of thelubricating oil composition for internal combustion engines is much morethan 12.5 mm²/s, the agitation resistance of the lubricating oilincreases in the internal combustion engine parts, and fuel efficiencyperformance worsens. If the kinematic viscosity at 100° C. is much lessthan 6.9 mm²/s, there is a possibility that metal contact may occur. Thekinematic viscosity at 100° C. is preferably 6.9 mm²/s or more, but lessthan 12.0 mm²/s, more preferably 6.9 mm²/s or more, but less than 9.3mm²/s, and furthermore preferably 6.9 mm²/s or more, but less than 7.5mm²/s. Within this range, a high fuel efficiency performance isobtainable under a condition of maintaining a high HTHS viscosity.

In the lubricating oil composition for internal combustion engines ofthe present invention, there is no particular limitation on the mixingratio of the lubricant base oil consisting of the mineral oil (A) and/orsynthetic oil (B) and the ethylene-α-olefin copolymer (C) if therequired properties in the objective uses are satisfied. However,normally, the mass ratio of the lubricant base oil and theethylene-α-olefin copolymer (C) (i.e. mass of lubricant base oil/mass ofcopolymer (C)) is 97/3 to 50/50.

Moreover, additives such as detergent dispersants, viscosity indeximproving agents, antioxidants, corrosion preventing agents, anti-wearagents, friction modifying agents, pour point lowering agents, anti-rustagents and anti-foamers may be contained in the lubricating oilcomposition for internal combustion engines of the present invention.

Below are exemplifications of additives which can be utilized in thelubricating oil composition of the present invention, where these can beused alone, or used in combination of two or more.

Exemplifications of the detergent dispersant include metal sulfonates,metal phenates, metal phosphonates, and imide succinate. Alkaline metalor alkaline earth metal salicylate-, phenate- or sulfonate-detergentsare preferred in the lubricating oil composition of the presentinvention. Specific exemplifications include sulfonates; phenate; orsalicylate of calcium or magnesium; imide succinate; and benzyl amine.The detergent dispersant may be used as required in a range of 0 to 15%by mass with respect to 100% by mass of the lubricating oil composition.

In addition to ethylene-α-olefin copolymers (excluding theethylene-α-olefin copolymer (C)), known viscosity index improving agentssuch as olefin copolymers whose molecular weights exceed 50,000,methacrylate-based copolymers and liquid polybutene can be used togetheras the viscosity index improving agent. The viscosity index improvingagent may be used as required in a range of 0 to 50% by mass withrespect to 100% by mass of the lubricating oil composition.

Examples of the antioxidant include phenol-based or amine-basedcompounds such as 2,6-di-t-butyl-4-methylphenol. The antioxidant may beused as required in a range of 0 to 3% by mass with respect to 100% bymass of the lubricating oil composition.

Examples of the corrosion preventing agent include compounds such asbenzotriazole, benzoimidazole, and thiadiazole. The corrosion preventingagent may be used as required in a range of 0 to 3% by mass with respectto 100% by mass of the grease composition.

Exemplifications of the anti-wear agent include inorganic or organicmolybdenum compounds such as molybdenum disulfide, graphite, antimonysulfide, and polytetrafluoroethylene. The anti-wear agent may be used asrequired in a range of 0 to 3% by mass with respect to 100% by mass ofthe lubricating oil composition.

Exemplifications of the friction modifying agent include aminecompounds, imide compound, fatty acid esters, fatty acid amides, andfatty acid metal salts having at least one alkyl group or alkenyl grouphaving 6 to 30 carbon atoms, particularly linear alkyl groups or linearalkenyl groups having 6 to 30 carbon atoms, in a molecule.

Exemplifications of the amine compound include a linear- or branched-,preferably linear-, aliphatic monoamine, or a linear- or branched-,preferably linear-, aliphatic polyamine having 6 to 30 carbon atoms, oralkylene oxide adducts of these aliphatic amines. Examples of the imidecompound include imide succinate with linear- or branched-alkyl group oralkenyl group having 6 to 30 carbon atoms and/or compounds thereofmodified by a carboxylic acid, boric acid, phosphoric acid, sulfuricacid etc. Exemplifications of the fatty acid ester include esters of alinear- or branched-, preferably linear-, fatty acid having 7 to 31carbon atoms with an aliphatic monohydric alcohol or aliphaticpolyhydric alcohol. Exemplifications of the fatty acid amide includeamides of a linear- or branched-, preferably linear-, fatty acid having7 to 31 carbon atoms with an aliphatic monoamine or aliphatic polyamine.Examples of fatty acid metal salts include alkaline-earth metal salts(e.g. magnesium salts and calcium salts) and zinc salts of a linear- orbranched-, preferably linear-, fatty acid having 7 to 31 carbon atoms.

The friction modifying agent may be used as required in a range of 0 to5.0% by mass with respect to 100% by mass of the lubricating oilcomposition.

A variety of known pour point lowering agents may be used as the pourpoint lowering agent. Specifically, high molecular compounds containingan organic acid ester group may be used, and in particular, vinylpolymers containing an organic acid ester group are suitably used.Examples of the vinyl polymer containing an organic acid ester groupinclude (co)polymers of methacrylic acid alkyl, (co)polymers of acrylicacid alkyl, (co)polymers of fumaric acid alkyl, (co)polymers of maleicacid alkyl, and alkylated naphthalene.

Such pour point lowering agents have a melting point of −13° C. orlower, preferably −15° C., and furthermore preferably −17° C. or lower.The melting point of the pour point lowering agent is measured by meansof differential scanning calorimetry (DSC). Specifically, a sample ofabout 5 mg is packed into an aluminum pan and temperature is raised to200° C., where the temperature is maintained at 200° C. for 5 minutes.This is then cooled at 10° C./minute until reaching −40° C., where thetemperature is maintained at −40° C. for 5 minutes. The temperature isthen raised at 10° C./minute during which the melting point is obtainedfrom the heat absorption curve.

The pour point lowering agent has a polystyrene conversion weightaverage molecular weight obtainable by gel permeation chromatography inthe range of 20,000 to 400,000, preferably 30,000 to 300,000, morepreferably 40,000 to 200,000.

The pour point lowering agent may be used as required in a range of 0 to2% by mass with respect to 100% by mass of the lubricating oilcomposition.

Examples of the anti-rust agent include compounds such as aminecompounds, carboxylic acid metal salts, polyhydric alcohol esters,phosphorus compounds, and sulfonates. The anti-rust agent may be used asrequired in a range of 0 to 3% by mass with respect to 100% by mass ofthe lubricating oil composition.

Exemplifications of the anti-foamer include silicone-based compoundssuch as dimethyl siloxane and silica gel dispersions, and alcohol- orester-based compounds. The anti-foamer may be used as required in arange of 0 to 0.2% by mass with respect to 100% by mass of thelubricating oil composition.

In addition to the aforementioned additives, anti-emulsifying agents,coloring agents, oiliness agents (oiliness improving agents) and thelike may also be used as required.

In the lubricating oil for internal combustion engines, the so-called DIpackage is industrially supplied, where in the DI package, all types ofnecessary additives are formulated for this use, and then concentratedand dissolved in lubricating oil such as mineral oil or synthetichydrocarbon oil. Such a DI package can also be applied to thelubricating oil composition of the present invention.

<Use>

The lubricating oil composition of the present invention can be suitablyutilized in internal combustion engine oil. Since a high HTHS viscosityis obtainable, a lowered viscosity within the same viscosity standard asthat of the SAE is possible, and hence the lubricating oil compositionof the present invention can be suitably utilized as fuel efficientengine oil in automobiles.

EXAMPLES

The present invention is further specifically explained based on thebelow Examples. However, the present invention is not limited to theseExamples.

[Evaluation Method]

In the below Examples and Comparative Examples etc., the physicalproperties etc. of the ethylene-α-olefin copolymer and the lubricatingoil composition for internal combustion engine oil were measured by thebelow methods.

<Ethylene Content (Mol %)>

Using a Fourier transform infrared spectrometer FT/IR-610 or FT/IR-6100(made by JASCO), the absorbance ratio of the absorption in the vicinityof 721 cm⁻¹ based on the horizontal vibration of the long chainmethylene group, and the absorption in the vicinity of 1155 cm⁻¹ basedon the skeletal vibration of propylene (D1155 cm⁻¹/D721 cm⁻¹) wascalculated, and the ethylene content (% by weight) was obtained by thecalibration curve created beforehand (created using the ASTM D3900reference sample). Using the ethylene content (% by weight) thusobtained, the ethylene content (mol %) was obtained according to thefollowing Formula.

${{Ethylene}\mspace{14mu}{content}\mspace{14mu}\left( {{mol}\mspace{14mu}\%} \right)} = \frac{\left\lbrack {{ethylene}\mspace{14mu}{content}\mspace{14mu}{\left( {\%\mspace{14mu}{by}\mspace{14mu}{weight}} \right)/28}} \right\rbrack}{\begin{matrix}{\left\lbrack {{ethylene}\mspace{14mu}{content}\mspace{14mu}{\left( {\%\mspace{14mu}{by}\mspace{14mu}{weight}} \right)/28}} \right\rbrack +} \\\left\lbrack {{propylene}\mspace{14mu}{content}\mspace{14mu}{\left( {\%\mspace{14mu}{by}\mspace{14mu}{weight}} \right)/42}} \right\rbrack\end{matrix}}$

<B-Value>

Employing o-dichloro benzene/benzene-d6 (4/1 [vol/vol %]) as ameasurement solvent, the ¹³C-NMR spectrum was measured under themeasuring conditions (100 MHz, ECX 400P, made by JEOL Ltd) oftemperature of 120° C., spectral width of 250 ppm, pulse repeating timeof 5.5 seconds, and a pulse width of 4.7 μsec (45° pulse), or under themeasuring conditions (125 MHz, AVANCE III Cryo-500 made by BrukerBiospin Inc) of temperature of 120° C., spectral width of 250 ppm, pulserepeating time of 5.5 seconds, and a pulse width of 5.0 μsec (45°pulse), and the B-value was calculated based on the following Formula[1].

$\begin{matrix}{B = \frac{P_{OE}}{2{P_{O} \cdot P_{E}}}} & \lbrack 1\rbrack\end{matrix}$

In Formula [1], PE indicates the molar fraction contained in theethylene component, Po indicates the molar fraction contained in theα-olefin component, and POE indicates the molar fraction of theethylene-α-olefin sequences of all dyad sequences.

<Molecular Weight Distribution>

Employing the HLC-8320 GPC (gel permeation chromatography) deviceproduced by Tosoh Corporation, the molecular weight distribution wasmeasured as below. Four TSK gel Super Multipore HZ-M columns were usedas separation columns, the column temperature was 40° C.,tetrahydrofuran (made by Wako Pure Chemical Industries) was used as themobile phase, with a development rate of 0.35 ml/minute, a sampleconcentration of 5.5 g/L, a sample injection amount of 20 microliters,and a differential refractometer was used as a detector. PStQuick MP-M;made by Tosoh Corporation) was used as the reference polystyrene. Inaccordance with general-purpose calibration procedures, weight averagemolecular weight (Mw) and number average molecular weight (Mn) werecalculated in terms of polystyrene molecular weight, and the molecularweight distribution (Mw/Mn) was calculated from those values.

<Viscosity Properties>

The 100° C. kinematic viscosity and the viscosity index was measured andcalculated by the method described in JIS K2283.

<HTHS Viscosity>

The HTHS viscosity was measured at 150° C. by the method described inASTM D4683.

<CCS Viscosity>

The CCS viscosity was measured at −25° C., −30° C. and −35° C. by themethod described in ASTM D5293.

<Thermal and Oxidation Stability>

Regarding thermal and oxidation stability, a test was conducted inaccordance with the Oxidation Stability Test of Lubricating Oil forInternal Combustion Engines (ISOT) method described in JIS K2514, andthe lacquer rating was evaluated 72 hours after the test time.

Production of ethylene-α-olefin Copolymer (C)

Ethylene-α-olefin copolymers (C) were prepared in accordance with thePolymerization Examples below.

Polymerization Example 1

250 mL of heptane was charged into a glass polymerization vessel with avolume of 1 L sufficiently substituted with nitrogen, and thetemperature in the system was raised to 50° C., and then 25 L/h ofethylene, 75 L/h of propylene, and 100 L/h of hydrogen were continuouslysupplied into the polymerization vessel, and stirred with a rotation of600 rpm. Then, 0.2 mmol of triisobutyl aluminum was charged into thepolymerization vessel, and 0.023 mmol of N,N-dimethylanilinium tetrakis(pentafluorophenyl) borate and 0.00230 mmol of diphenylmethylene[η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butyl fluorenyl)]zirconium dichloride, which were pre-mixed in toluene for 15 minutes ormore, were charged into the polymerization vessel to start thepolymerization. Ethylene, propylene and hydrogen were then continuouslysupplied, and polymerization took place at 50° C. for 15 minutes.Polymerization was stopped by adding a small amount of isobutyl alcoholin the system, and the unreacted monomers were purged. The resultingpolymer solution was washed 3 times with 100 mL of a 0.2 mol/L solutionof hydrochloric acid, further washed 3 times with 100 mL of distilledwater, dried with magnesium sulfate, and the solvent was then distilledoff under reduced pressure. The resulting polymer was dried overnight at80° C. under reduced pressure to obtain 1.43 g of an ethylene-propylenecopolymer. The resulting polymer had an ethylene content of 52.4 mol %,an Mw of 13,600, an Mw/Mn of 1.9, a B-value of 1.2, and a 100° C.kinematic viscosity of 2,000 mm²/s.

Polymerization Example 2

250 mL of heptane was charged into a glass polymerization vessel with avolume of 1 L sufficiently substituted with nitrogen, and thetemperature in the system was raised to 50° C., and then 25 L/h ofethylene, 75 L/h of propylene, and 100 L/h of hydrogen were continuouslysupplied into the polymerization vessel, and stirred with a rotation of600 rpm. Then, 0.2 mmol of triisobutyl aluminum was charged into apolymerization vessel, and 0.688 mmol of MMAO and 0.00230 mmol ofdimethylsilyl bis(indenyl) zirconium dichloride, which were pre-mixed intoluene for 15 minutes or more, were charged into a polymerizationvessel to start the polymerization. Ethylene, propylene and hydrogenwere then continuously supplied, and polymerization took place at 50° C.for 15 minutes. Polymerization was stopped by adding a small amount ofisobutyl alcohol in the system, and the unreacted monomers were purged.The resulting polymer solution was washed 3 times with 100 mL of a 0.2mol/L solution of hydrochloric acid, further washed 3 times with 100 mLof distilled water, dried with magnesium sulfate, and the solvent wasthen distilled off under reduced pressure. The resulting polymer wasdried overnight at 80° C. under reduced pressure to obtain 1.43 g of anethylene-propylene copolymer. The resulting polymer had an ethylenecontent of 52.1 mol %, an Mw 13,800, an Mw/Mn of 2.0, a B-value of 1.2,and a 100° C. kinematic viscosity of 2,000 mm²/s.

The copolymer obtained by Polymerization Example 1, and the copolymerobtained by Polymerization Example 2, are respectively described belowas Polymer 1 and Polymer 2.

[Preparation of Lubricating Oil Composition for Internal CombustionEngines]

The components used other than the ethylene-α-olefin copolymer (C) inthe preparation of the below lubricating oil compositions are asfollows.

Lubricant base oil; The below lubricant base oils were used as thesynthetic oil (B).

Synthetic oil-A: a synthetic oil poly-α-olefin with a 100° C. kinematicviscosity of 4.0 mm²/s, a viscosity index of 123, and a pour point of−60° C. or lower (NEXBASE 2004, made by Neste)

Synthetic oil-B: a synthetic oil poly-α-olefin with a 100° C. kinematicviscosity of 5.8 mm²/s, a viscosity index of 138, and a pour point of−60° C. or lower (NEXBASE 2006, made by Neste)

Synthetic oil-C: diisodecyl adipate, a fatty acid ester with a 100° C.kinematic viscosity of 3.7 mm²/s, a viscosity index of 156, and a pourpoint of −60° C. or lower (made by Daihachi Chemical Industry Co., Ltd.)

DI package (DI);

P-5202 made by Infineum

Olefin copolymer (OCP);

M-1710 made by LUBRIZOL Japan. Dilution of a high molecular weight OCP(kinematic viscosity at 100° C. not measureable) in mineral oil, as aviscosity index improving agent for regular automobiles.

Polymethacrylate (PMA);

AC-1703 made by Sanyo Chemical. Dilution of a high molecular weight PMA(kinematic viscosity at 100° C. not measureable) in mineral oil, as aviscosity index improving agent for regular automobiles. Thispolymethacrylate has a pour point lowering capability.

<Lubricating Oil Composition for Internal Combustion Engines> Example 1

Synthetic oil-A and Synthetic oil-C, which are the Synthetic oil (B),were used as the lubricant base oil, and the copolymer obtained inPolymerization Example 1 (Polymer 1) was used as the ethylene-α-olefincopolymer (C). These were mixed together in the usual manner with the DIpackage (DI), thereby preparing a lubricating oil composition forinternal combustion engine oil. The addition amounts of the respectivecomponents and the physical properties etc. of the resulting lubricatingoil compositions are as shown in Table 3.

Examples 2 to 5, Comparative Examples 1 to 5

Except for changing the types of components and addition amounts tothose as described in Table 3, the lubricating oil compositions wereprepared in the same way as in Example 1. The physical properties etc.of the resulting lubricating oil compositions are as shown in Table 3.

TABLE 3 Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 ex.1 ex. 2 ex. 3 ex. 4 ex. 5 Polymer 1 % by 4.0 6.0 8.0 4.0 6.0 massPolymer 2 % by 4.0 6.0 8.0 mass OCP % by 6.8 mass PMA % by 4.3 massSynthetic oil - A % by 65.0 63.0 61.0 65.0 63.0 61.0 62.2 64.7 massSynthetic oil - B % by 65.0 63.0 mass Synthetic oil - C % by 20.0 20.020.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 mass DI % by 11.0 11.0 11.0 11.011.0 11.0 11.0 11.0 11.0 11.0 mass 100° C. kinematic mm²/s 7.6 9.2 11.09.7 11.5 7.6 9.1 11.2 8.0 8.0 viscosity Viscosity index — 165 170 171158 161 165 170 172 HTHS viscosity mPa·s 2.79 3.33 3.94 3.20 3.75 2.402.35 −25° C. CCS mPa·s 4,300 viscosity −30° C. CCS mPa·s 4,000 5,3005,800 viscosity −35° C. CCS mPa·s 5,200 viscosity ISOT Varnish AdheredAdhered Adhered Adhered Adhered Adhered Adhered Adhered rating substancesubstance substance substance substance substance substance substance(thin) (thin) (thin) (thin) (thin) (thick) (thick) (thick)

1. A lubricating oil composition for internal combustion engines,comprising a lubricant base oil, and 3% by mass or more, but less than40% by mass of a liquid random copolymer (C) of ethylene and α-olefin,the liquid random copolymer (C) being prepared by the below method (α),the lubricating oil composition having a kinematic viscosity at 100° C.of 6.9 mm²/s or more, but less than 12.5 mm²/s, wherein the lubricantbase oil consists of a mineral oil (A) having the properties of thebelow (A1) to (A3), and/or a synthetic oil (B) having the properties ofthe below (B1) to (B3). (A1) The mineral oil has a kinematic viscosityat 100° C. of 2 to 7 mm²/s. (A2) The mineral oil has a viscosity indexof 105 or more. (A3) The mineral oil has a pour point of −10° C. orlower. (B1) The synthetic oil has a kinematic viscosity at 100° C. of 1to 7 mm²/s. (B2) The synthetic oil has a viscosity index of 120 or more.(B3) The synthetic oil has a pour point of −30° C. or lower. (Method(α)) A method (α) for preparing a liquid random copolymer of ethyleneand α-olefin, comprising a step of carrying out solution polymerizationof ethylene and α-olefin having 3 to 20 carbon atoms, under a catalystsystem comprising (a) a bridged metallocene compound represented by thefollowing Formula 1, and (b) at least one compound selected from a groupconsisting of (i) an organoaluminum oxy-compound, and (ii) a compoundwhich reacts with the bridged metallocene compound to form an ion pair.

[In Formula 1, R¹, R², R³, R⁴, R⁵, R⁸, R⁹ and R¹² are respectively andindependently hydrogen atom, hydrocarbon group or silicon-containinghydrocarbon group, and adjoining groups are optionally connected to eachother to form a ring structure, R⁶ and R¹¹, being the same, are hydrogenatom, hydrocarbon group or silicon-containing hydrocarbon group, R⁷ andR¹⁰, being the same, are hydrogen atom, hydrocarbon group orsilicon-containing hydrocarbon group, R⁶ and R⁷ are optionally connectedto hydrocarbon having 2 to 3 carbon atoms to form a ring structure, R¹¹and R¹⁰ are optionally connected to hydrocarbon having 2 to 3 carbonatoms to form a ring structure, R⁶, R⁷, R¹⁰ and R¹¹ are not hydrogenatom at the same time; Y is a carbon atom or silicon atom; R¹³ and R¹⁴are independently aryl group; M is Ti, Zr or Hf; Q is independentlyhalogen, hydrocarbon group, an anionic ligand or a neutral ligand whichcan be coordinated to a lone pair of electrons; and j is an integer of 1to 4.]
 2. The lubricating oil composition for internal combustionengines according to claim 1, wherein in the metallocene compoundrepresented by the above Formula 1, at least one among substituents (R¹,R², R³ and R⁴) bonded to a cyclopentadienyl group, is a hydrocarbongroup having 4 or more carbon atoms.
 3. The lubricating oil compositionfor internal combustion engines according to claim 1, wherein R⁶ andR¹¹, being the same, are hydrocarbon groups having 1 to 20 carbon atoms.4. The lubricating oil composition for internal combustion enginesaccording to claim 1, wherein in the metallocene compound represented bythe above Formula 1, substituent (R² or R³) bonded to the 3-position ofthe cyclopentadienyl group is a hydrocarbon group.
 5. The lubricatingoil composition for internal combustion engines according to claim 4,wherein in the metallocene compound represented by the above Formula 1,the hydrocarbon group (R² or R³) bonded to the 3-position of thecyclopentadienyl group is an n-butyl group.
 6. The lubricating oilcomposition for internal combustion engines according to claim 1,wherein in the metallocene compound represented by the above Formula 1,substituents (R⁶ and R¹¹) bonded to the 2-position and 7-position of thefluorenyl group are all tert-butyl groups.
 7. The lubricating oilcomposition for internal combustion engines according to claim 1,wherein the compound which reacts with the bridged metallocene compoundto form an ion pair is a compound represented by the following Formula6.

[In Formula 6, R^(e+) is H⁺, a carbenium cation, an oxonium cation, anammonium cation, a phosphonium cation, a cycloheptyltrienyl cation, or aferrocenium cation having a transition metal, and R^(f) to R^(i) each isindependently a hydrocarbon group having 1 to 20 carbon atoms.]
 8. Thelubricating oil composition for internal combustion engines according toclaim 7, wherein the ammonium cation is a dimethylanilinium cation. 9.The lubricating oil composition for internal combustion enginesaccording to claim 7, wherein the catalyst system further comprises anorganoaluminum compound selected from a group consisting of trimethylaluminum and triisobutyl aluminum.
 10. The lubricating oil compositionfor internal combustion engines according to claim 1, wherein theα-olefin of the liquid random copolymer (C) is propylene.
 11. Alubricating oil composition for internal combustion engines, comprisinga lubricant base oil, and 3% by mass or more, but less than 40% by massof a liquid random copolymer of ethylene and α-olefin, the liquid randomcopolymer having the properties of the below (C1) to (C5), thelubricating oil composition having a kinematic viscosity at 100° C. of6.9 mm²/s or more, but less than 12.5 mm²/s, wherein the lubricant baseoil consists of a mineral oil (A) having the properties of the below(A1) to (A3), and/or a synthetic oil (B) having the properties of thebelow (B1) to (B3). (A1) The mineral oil has a kinematic viscosity at100° C. of 2 to 7 mm²/s. (A2) The mineral oil has a viscosity index of105 or more. (A3) The mineral oil has a pour point of −10° C. or lower.(B1) The synthetic oil has a kinematic viscosity at 100° C. of 1 to 7mm²/s. (B2) The synthetic oil has a viscosity index of 120 or more. (B3)The synthetic oil has a pour point of −30° C. or lower. (C1) The liquidrandom copolymer comprises 40 to 60 mol % of ethylene units and 60 to 40mol % of α-olefin units having 3 to 20 carbon atoms. (C2) The liquidrandom copolymer has a number average molecular weight (Mn) of 500 to10,000 and a molecular weight distribution (Mw/Mn, Mw is the weightaverage molecular weight) of 3 or less, as measured by gel permeationchromatography (GPC). (C3) The liquid random copolymer has a kinematicviscosity at 100° C. of 30 to 5,000 mm²/s. (C4) The liquid randomcopolymer has a pour point of 30 to −45° C. (C5) The liquid randomcopolymer has a Bromine Number of 0.1 g/100 g or less.
 12. Thelubricating oil composition for internal combustion engines according toclaim 1, wherein the synthetic oil (B) contains an ester, and asynthetic oil other than esters.
 13. A method for producing alubricating oil composition for internal combustion engines, comprisingthe steps of: preparing a liquid random copolymer (C) of ethylene andα-olefin by the following method (α); and preparing a lubricating oilcomposition for internal combustion engines by mixing a lubricant baseoil and the liquid random copolymer (C) of an amount of 3% by mass ormore, but less than 40% by mass in the lubricating oil composition, thecomposition having a kinematic viscosity at 100° C. of 6.9 mm²/s ormore, but less than 12.5 mm²/s, wherein the lubricant base oil consistsof a mineral oil (A) having the properties of the below (A1) to (A3),and/or a synthetic oil (B) having the properties of the below (B1) to(B3). (A1) The mineral oil has a kinematic viscosity at 100° C. of 2 to7 mm²/s. (A2) The mineral oil has a viscosity index of 105 or more. (A3)The mineral oil has a pour point of −10° C. or lower. (B1) The syntheticoil has a kinematic viscosity at 100° C. of 1 to 7 mm²/s. (B2) Thesynthetic oil has a viscosity index of 120 or more. (B3) The syntheticoil has a pour point of −30° C. or lower. (Method (α)) A method (α) forpreparing a liquid random copolymer of ethylene and α-olefin, comprisinga step of carrying out solution polymerization of ethylene and α-olefinhaving 3 to 20 carbon atoms, under a catalyst system comprising (a) abridged metallocene compound represented by the following Formula 1, and(b) at least one compound selected from a group consisting of (i) anorganoaluminum oxy-compound, and (ii) a compound which reacts with thebridged metallocene compound to form an ion pair.

[In Formula 1, R¹, R², R³, R⁴, R⁵, R⁸, R⁹ and R¹² are respectively andindependently hydrogen atom, hydrocarbon group or silicon-containinghydrocarbon group, and adjoining groups are optionally connected to eachother to form a ring structure, R⁶ and R¹¹, being the same, are hydrogenatom, hydrocarbon group or silicon-containing hydrocarbon group, R⁷ andR¹⁰, being the same, are hydrogen atom, hydrocarbon group orsilicon-containing hydrocarbon group, R⁶ and R⁷ are optionally connectedto hydrocarbon having 2 to 3 carbon atoms to form a ring structure, R¹¹and R¹⁰ are optionally connected to hydrocarbon having 2 to 3 carbonatoms to form a ring structure, R⁶, R⁷, R¹⁰ and R¹¹ are not hydrogenatom at the same time; Y is a carbon atom or silicon atom; R¹³ and R¹⁴are independently aryl group; M is Ti, Zr or Hf; Q is independentlyhalogen, hydrocarbon group, an anionic ligand or a neutral ligand whichcan be coordinated to a lone pair of electrons; and j is an integer of 1to 4.]